A headrest folding device of the prior art has been suggested, for example, as disclosed in the Patent Literature 1 (Korea Registered Patent No. 10-1080313) that had been filed earlier by the applicant of this application.
The headrest folding device of the Patent Literature 1, as illustrated in FIG. 16, comprises: a housing 10 installed inside the back plate of a seat and provided with a pair of guide slots 12 at the same locations in the upper sides of both side plates 11 in a way that the upper portions thereof are open and respectively forming concentric circles with respect to a pair of hinge holes 13; a stay rod 20 whose back ends are fixed to the both sides of a horizontal portion 21 and the front end is pivotally installed to the housing 10 through a pair of hinge plates 23 which are shaft-coupled to the hinge holes 13 via a pair of hinge shafts 24 respectively; a supporting member 30 mounted inside with a supporting plate 31 wherein a pair of guide holes 311 for inserting both front ends of a pair of vertical portions; a holding member 40 which is shaft installed in the inner surface of a side plate 11 via a holding shaft 40b so as to be rotated in the opposite direction of the stay rod 20 due to the repulsive force of a holding spring 40a, and wherein a holding slot 41 is formed in the upper portion for holding the horizontal portion 21 of the stay rod 20 which is erected through upward rotation when the supporting member is being pushed upward, and a holding threshold 42 is formed in the lower end; a stopping member 50 which is shaft installed in the lower side of the inner surface of a side plate 11 with a stopping shaft 50b so as to be rotated in the opposite direction of the holding member 40 due to the repulsive force of a stopping spring 50a, and wherein a stopping threshold 51 is installed in the upper end for maintaining the erected state of the stay rod 20 by holding the holding threshold 42 when the holding member 40 is holding the horizontal portion 21 of the erected stay rod 20; a wire 60 whose one end is coupled to the back end of the stopping member 50 and the other end is installed through coupling with a lever (not shown) which is installed in the outer side of the back plate so that the stopping of the holding member 40 is released by pulling the stopping member 50 and rotating it in the opposite direction of the repulsive force of the stopping spring 50a when the lever is manipulated; a main spring 70 which is coupled to the hinge shaft 24 and one end is hanged on the horizontal portion 21 of the stay rod 20 while the other end is hanged on the other side plate 11 of the housing 10 so that the erected stay rod 20 is forwardly and downwardly rotated and bended due to the reaction of the repulsive force when the stopping of the holding member 40 by the stopping member 50 is released; and a link 80 whose front end is shaft coupled to a hinge plate 4 which is additionally installed in the lower middle of the supporting plate 31 via a line shaft 81 and the back end is shaft coupled to the upper end of a bracket 10a installed in the middle back side of the housing 10 via a line shaft 81′ so as to be located in the upper back side than the hinge shaft 24.
The unexplained symbols 14 and 14′ represent the shaft holes of the stopping shaft 50b; 17 represents a supporting plate, 16 represents communicating hole of the wire 60; 15 represents a lower surface plate; 11a represents the shaft hole of the line shaft 81′; and 43 represents the supporting threshold.
In such Patent Literature 1, since the horizontal portion 21 of the stay rod 20 is being held in the holding slot 41 of the holding member 40, the force, being applied to the stay rod 20 continuously in the direction of folding, is directly transferred to the holding member 40, therefore the releasing from the holding slot 41 through the rotation of the holding member 40 becomes very stiff.
Such stiff rotation of the holding member 40 directly affects the pulling of the braking member 50, and therefore, a user cannot pull the wire 60 smoothly.
Similarly, in Patent Literature 2 (Korea Registered Patent No. 10-0943327) illustrated in FIG. 17, a hanger portion 120 is disposed in the horizontal portion of the stay rod 110, and a stopper 130 is disposed in the hanger portion 120 whereon the stopping protrusion 131 is caught, therefore the pulling of the stopper 130 is not smooth due to the posture of the stay rod 110 tending to be folded.
In this way, since the braking member or the stopper must directly release the holding of the stay rod in order to switch from the unfolding state to the folding state, therefore a large load is imposed thereon making smooth operation difficult and generating noise too.
Also, since the holding member 40 or the stopper 130 is directly holding the stay, there is limitation in enhancing the strength of the headrest under the state of locking. The shape cannot be changed since the shape of the cross-section of the stay rod is determined to be a circular shape and because of the externally exposed area. Moreover, even the thickness and the size of the stay are changed, it is not practical since the weight and the size will be increased thereby.
Meanwhile, ‘tip-up linkage type folding headrest device’ of Patent Literature 3 adopts a structure wherein a fixed cam 301 is engaged with a rotating cam 305 as illustrated in FIG. 18.
That is, the fixed cam 301 is not directly locking to the stay 31.
However, when the rotating cam 305 is self-rotating, the stay 31, which is fixed only to the rotating cam 305, is being rotated together.
In such rotation of the stay 31 without a rotation radius of the stay 31, the vertical frame 310 of the stay 31 is pivotally rotated.
The vertical frame 310 is exposed through the slot formed in the upper end of the seat back.
Therefore, since the rotation amount of such pivot type rotation is large, the length of the slot in the seat back along the front to rear direction becomes longer, which is not desirable in the aspects of appearance.